The development of size variation in Dover sole,Solea soleaand turbot,Scophthalmus maximus: genetic variability between different geographical and among year class farmed strains

Abstract

Growth and variation in size of turbot and sole larvae originating from different genetic sources were compared at different stocking densities, including genetically based information that might lead to a better knowledge of heterogeneity in cultivated populations. There was no effect of density on growth rate in either species. However, between the two sole batches there was an earlier metamorphosis of faster growing fish from Norway. In sole groups after metamorphosis, variation was stable and therefore no development of size variation was observed. There was no density effect on size variation within turbot batches before, or after metamorphosis. Spreading rate and growth rate were positively correlated in sole larvae indicating that growth of the smaller fish was not equal to the larger ones, but size variation followed a different pattern in turbot. No evidence for either overall significant heterozygosity excess, or deficiency was evidenced in the farmed strains of either species. However, significant differences between farmed populations in terms of genetic variability (θ) were reported, which was rather attributed to within differentiation than between strains. One could safely argue that different strains of Dover sole originated from different genetic sources (factorial analysis). Moreover, when the analysis was extended to individual loci to assess whether specific loci had any consistently larger, or smaller effect on heterozygosity, locus specific significant trends were discerned in turbot. A positive Heterozygosity Fitness (growth rate) Correlation (HFC) suggests that heterozygotes reported enhanced growth rates compared with homozygous ones in flatfish larvae, thus special precautions should be taken into account whenever different genetic structure patterns emerge, because of various flatfish broodstock geographical origin and year class samples.